The fuel and lubrication oil which are used in an internal combustion engine contain sulfur. Therefore, the exhaust gas contains SOx. In this regard, this SOx acts to greatly reduce the performance and durability of the exhaust gas purification catalyst and other post-treatment devices which are arranged inside of the engine exhaust passage. Therefore, the SOx in the exhaust gas is preferably removed.
Therefore, there is known an internal combustion engine which arranges inside an engine exhaust passage an SOx trap catalyst which can trap the SOx which is contained in the exhaust gas (see Patent Literature 1). Inside this SOx trap catalyst, mainly an alkali metal is carried dispersed. When the air-fuel ratio of the exhaust gas which flows into the SOx trap catalyst is lean, the SOx which is contained in the exhaust gas reacts with the nitrates which are present at the surface part of the SOx trap catalyst and is trapped in the form of sulfates. On the other hand, in this internal combustion engine, when the sulfates at the surface part of the SOx trap catalyst increase and the SOx trap rate starts to fall, the temperature of the SOx trap catalyst is held at the melting point of the nitrates of the alkali metal or more whereby the nitrates inside the SOx trap catalyst move to the SOx trap catalyst surface and concentrate there. If the nitrates concentrate at the SOx trap catalyst surface, the SO2 in the exhaust gas reacts with the concentrated nitrates and is trapped well in the form of sulfates. Due to this, the NOx trap rate is restored.